Smoke sensors generally sense the presence of smoke within a chamber between an emitter and a detector. FIG. 1A is a schematic diagram of a first prior art smoke detector 100. Smoke particles enter an optical chamber 130. The chamber is mounted on a case molding 137, and covered by a cover 135. The smoke enters the optical chamber through a series of baffles 170. The baffles are shaped to allow ingress of smoke into the optical chamber, but to block direct ingress of light from nearby light sources. Smoke particles in the path of an emitter 120 are illuminated by light produced by the emitter 120, and the illuminated smoke particles scatter the light which is then detected by the detector 110. The emitter 120 and detector 110 are located inside the optical chamber. FIG. 1B is a simplified diagram of the prior art smoke detector, showing an angle α between the orientation of the detector 110 and the emitter 120. The emitter 120 and detector 110 are oriented at the angle α to prevent light emitted from the emitter 120 from projecting directly into the detector 110. The angle α is typically on the order of 135 degrees. Therefore, the detector 110 will only detect light from the emitter 120 when the emitted light is scattered in a diffuse manner by discrete smoke particles within the chamber 130. However, since the emitter 120 and detector 110 are physically located within the chamber 130, as shown by FIG. 1C, they may block the ingress of smoke entering the chamber 130 from some directions, thereby increasing the detection time.
It should be noted that many constraints are placed on the designs of smoke cells by regionally specific manufacturing and/or usage standards documents, for example, Deutsche Norm Din En 14604.
FIG. 2 shows a second prior art smoke cell 200, where a smoke chamber 230 is formed by a housing having series of baffles 270 and a ceiling 260, mounted directly to a printed circuit board (PCB) 250. An emitter 220 and a detector 210 are mounted to an optic block 240, where the optic block 240 is mounted to the PCB 250, inside the smoke chamber 230. The optic block 240 is configured so the angle between the emitter 220 and the detector 210 may be on the order of 135 degrees. However, the location of the optic block 240 within the smoke chamber 230 may physically block smoke from entering the smoke chamber 230.
Therefore, there is a need in the industry to address the shortcomings described above.